Fine scale surgery, e.g. for placing implants at a spinal column, demands a high degree of positional accuracy. However with minimally invasive surgery, direct visual control of positioning of any instruments used by the surgeon is rather difficult. Sufficient visual control can often only be achieved by use of dedicated equipment, in particular picture generating devices, e.g. C-arm providing fluoroscopic control and/or sophisticated navigation systems forming a part of the operating room. However, such sophisticated navigation systems are expensive, complex to operate and as a result sparsely available and used. C-arm devices, on the other hand, are more readily available and surgeons are accustomed to their usage. However, continued use of the C-arm device provides rather a high radiation dose. Further, most C-arms have only one direction of view and consequently require intraoperative repositioning quite often, which can be detrimental to positional accuracy and is time consuming.
In order to provide a device which is easier to use and still provides an improved positional accuracy a handheld surgical tool was developed which features an autonomous navigation device (U.S. Pat. No. 8,057,482 B2). The tool features a button which has to be pressed when the device achieves its basic reference position. Thereby all positional data are set to zero. Once this is accomplished, the tool can be freely manipulated by the surgeon, and it will show its positioning in space on three numerical displays provided at its casing. The displays show three-dimensional angular orientation of the tool in space. This device is in an improvement in terms of determine positioning of the tool in an area with limited access and consequently restricted visual observance. However, it can be rather difficult for the surgeon to control the plurality of displays in order to check whether a desired orientation has already been reached or is maintained.